When controlling the movement of a webs of material which are transparent to a different degree using an optical sensor, different signal deviations of the sensor are obtained as a function of the transparency of the material between the bright value (with a sensor completely uncovered) and a dark value (the sensor is completely covered by the respective web of material). Therefore, in known devices for controlling web movement, variable settings are required when changing material to set the working point of web movement control to the respective material.
Frequently a sensor is soiled during operation. As a result, signal deviation varies and control is adversely affected.